All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
Permanent genetic modification of plants requires the introduction of new genetic material into the genome of a plant cell, a process called transformation. Uniform, non-chimeric, permanent genetic modification of plants requires the introduction of new genetic material into the genome of a plant cell followed by the regeneration of an entire plant from that one cell. Uniform, non-chimeric, permanent genetic modification of plants can arise from the introduction of new genetic material into the nuclear genome, mitochondria or chloroplasts. Since there are multiple copies of the organelles in each cell, considerable additional care must be taken to ensure that all such organelles are direct descendants of the originally altered organelle. Most plant transformations are therefore designed to target the nuclear genome, and require integration of the new genetic material into a chromosome, where it becomes a new, permanent, gene locus.
To accomplish this, methods must be developed to introduce DNA past several physical barriers, specifically: the plant cell wall, the cell membrane and the nuclear envelope. The plant cell wall deserves particular mention because unlike animal cell walls, which have extremely thin walls, plant cell walls form an extremely thick (ca. 20 nanometers), rigid structure comprised of cellulose fibrils encased in a cement of polysaccharide and proteins. Plant transformation therefore requires specialized methods for plant cell wall penetration that differ from those used for animal cell transformation, which typically involves direct DNA transfer methods.